In the early molding prior art, simple parts could be molded by laying up the prepreg composite material selectively in a female mold, and then positioning the male mold within the female mold to apply pressure to the laid-up composite material, then placing the mold so assembled in an autoclave and curing the composite material under both heat and pressure. This early method produced a single, simple composite part whose outer periphery is defined by the contours of the female mold, and whose inner periphery is defined by the contours of the male mold. The composite material could as well have been laid up on the male mold in this early prior art process.
Eventually, a vacuum bag replaced one of the molds, usually the male mold, and when under vacuum, produced pressure on the prepreg laid-up composite material in the female mold to cause it to closely conform to the shape of the female mold, and, i.e., to debulk the composite material, during the curing process in the autoclave where heat and more pressure are used.
In the prior art, methods have been taught to produce a mold, which is a faithful reproduction of a complex surface. Typical of this prior art are U.S. Pat. No. 3,369,949 of N. Forrest and U.S. Pat. No. 4,557,779 of Bower et al.
In U.S. Pat. No. 3,369,949 to N. Forrest, issued Feb. 20, 1968, it was desired to produce a mold which would simulate a complex surface, such as corduroy cloth. This was done by laying the corduroy cloth on a flat horizontal surface, applying a separator to it, and then coating the cloth and separator with an elastomeric material, such as silicone rubber. Forrest then places a strengthening fabric over the first silicone layer, and a second silicone layer is laid up over the strengthening fabric. The entire assembly is cured to provide a negative mold to simulate the corduroy cloth. If the teaching of Forrest were applied to the problem which our invention addresses, it would be necessary to fabricate the individual panels of our complex part individually and then attach them together mechanically thereafter.
U.S. Pat. No. 4,577,779 to Bower et al, issued Dec. 10, 1985, similarly teaches producing a mold to be able to reproduce a textured surface. In Bower et al, the textured surface to be simulated is sealed, a release agent is applied over the sealed surface, and epoxy prepreg sheets are laid up thereon and cured such that, when removed following curing, a mold has been formed capable of reproducing the textured surface. Bower et al, like Forrest, does not attack the problem of producing a complicated product made of composite material and consisting of a series of panels oriented in diverse angular relationship. Forrest or Bower et al teach producing a single panel. To obtain the type of article which is produced following the teachings of our invention, several of these panels would have to be mechanically connected which would result in a very labor intensive, expensive and heavy construction.
As composite parts became more complicated, it was necessary to include additional parts such as strengtheners, called details, to the basic composite part. These details were preformed, but not precured, and then hand positioned against the laid-up prepreg layers as these layers are supported in a female mold. These details were difficult to hand position and experience showed that the application of vacuum by the vacuum bag caused the details to drift out of proper position.
To overcome this problem, an expandable male mold was devised, which had selected contours in it to receive the preformed, but not precured, details and bring them into proper position and contact with the laid-up prepreg layers of the female mold such that, following debulking and co-curing of the part and its details, a composite part with the details forming part thereof was produced. This is the subject matter of pending application Ser. No. 128,134 by Dublinski et al filed Sep. 8, 1987, abandoned in favor of continuing application U.S. Ser. No. 576,176 filed Aug. 30, 1990 which has issued as U.S. Pat. No. 5,071,338.
As parts which are to be made of composite material, became more complicated by the addition of transverse bulkheads, intermediate decks, "T" attaching blades and return flanges, it was not possible to produce them by these prior art processes, unless the various components were to be made individually and then mechanically fastened together, which would have resulted in a time consuming, expensive and heavy final product.